1. Field of the Invention
The present invention relates to a semiconductor integrated circuit (hereinafter referred to "IC") device having a multi-level wiring structure and to a method of manufacturing the same.
2. Description of Related Art
To realize an IC device of high operation speed and high integration density, fine pattern and shallow P-N junction techniques have been widely used. An unit element such as a transistor in the IC device formed by the techniques, however, has inevitably a small capability for operating a load, that is, a wiring load in the IC. In recent, the tendency has been increased, and therefore, how to reduce the wiring load becomes a serious problem.
The wiring load is determined by resistance of wiring itself, and by parasitic capacitances between wiring and substrate and between mutual wirings. To reduce the resistance, the cross-sectional area of the wiring is necessary to be large value, but it is contrary to the recent miniaturization. To reduce the parasitic capacitance, an intermediate insulating layer is necessary to be made of a material having a low dielectric constant (relative dielectric constant) (.epsilon.'). However, the intermediate insulating layer of the IC device must satisfy various requirements such as good insulation, good covering, chemical stability and strong resistance to moisture. Therefore, a material which has a low dielectric constant cannot be soon employed in IC device in place of a silicon oxide film (.epsilon.'=3.9 to 4.0) and a silicon nitride film (.epsilon.'=7.8 to 8.0) which are now widely used. For example, a silicon organic compound film and a polyimide film can be formed by a spin-coating method and have a low dielectric constant (.epsilon.') of 2.0 to 3.0, and therefore, these films are recently paid attention to as an intermediate insulating layer. However, these organic series films lack chemical stability and resistance to moisture comparing with silicon oxide and silicon nitride films formed, for example, by a Chemical Vapor Deposition (hereinafter referred to "CVD") method. Therefore, if the latter is merely replaced by the former, the reliability of the wiring structure is decreased.